Die-Forging of Copper Forgings with Preliminary Forming of ... · corresponds largely to one of the principles of design of energy efficient die-forging technologies – the ... final

HCTL Open International Journal of Technology Innovations and Research (IJTIR) http://ijtir.hctl.org Volume 14, April 2015 e-ISSN: 2321-1814, ISBN (Print): 978-1-62951-946-3

V.V. Kukhar, V.A. Burko, O.V. Vasylevskyi and R.S. Nikolenko Page 1 Die-Forging of Copper Forgings with Preliminary Forming of Work-Piece Barrel Profile.

Die-Forging of Copper Forgings with Preliminary Forming of Work-Piece Barrel Profile V.V. Kukhar1, V.A. Burko 2, O.V. Vasylevskyi3, R.S. Nikolenko4 [email protected], [email protected], [email protected], [email protected] Abstract The advisability of combining of operations of preliminary upsetting and broaching of billets outside of dies impressions with the operations of subsequent finishing die-forging at manufacturing of axially asymmetric forgings was substantiated. The operations could be performed on different equipment, but the necessity of taking into account the peculiarities of the barrel shape of forgings during the preliminary upsetting prior to the subsequent die-forging passes being shown. Generalized method of designing of the processes of combined die-forging of axially asymmetric copper forgings was proposed with takes into account the regularities of shape alternation at the operations of upsetting and broaching. More advanced technologies of hot die-forging of copper forgings like “Nozzle” and “Oxygen lance head” type were implemented in industry condition, it allowing achieving 7.7 % saving of industrial (technical) copper per each single part. Keywords Axially Symmetric Copper Forgings, Preliminary Upsetting, Broaching, Hot Die-Forging, Barrel Profile.

Introduction Axially symmetric forgings, manufactured with application of operations of preliminary upsetting of ends are rather common products stamped on crankshaft hot stamping presses. Such forgings, included into the first class of the appropriate classification [1] are usually manufactured in open and closed dies.

1Dr.Sc., Professor, Chief of Metal Forming Department, SHEI “Priazovskyi State Technical University”, Mariupol, Ukraine.

2Ph.D., Professor Assistant, Department of Industrial Safety and Environment Protection, SHEI “Priazovskyi State Technical University”, Mariupol, Ukraine.

3Chief Technologist, Company Ltd. “METINVEST - Mariupol Mechanical Repair Plant”, Mariupol, Ukraine.

4Post Graduate Scholar, Metal Forming Department, SHEI “Priazovskyi State Technical University”, Mariupol, Ukraine.



Forgings made of copper and copper alloys are quite frequently met among parts with round shape. The design of technological processes of die-forging of pieces, made of ferrous metals should be realized with due regard to technological and thermal-physic properties of billets’ material in order to prevent their destruction and subcooling and include the analysis of variants of parts manufacturing, ensuring minimal metal and labour expenses [2].

The design of technological processes of die-forging of forgings, made of non-ferrous metals and alloys should be performed with due regard to technological and thermalphysic properties of forgings material in order to eliminate their destruction and subcooling and include the analysis of variants of parts manufacturing with minimal metal and labour expenses [2]. Here, while performing the choice of die-forging passes and designing die impressions the regularities of material deformation at specified deformation chart and thermal-and mechanical conditions must be taken into account. Application of the operation of free upsetting of forgings at the stage of technological design requires taking into account the regularities of formation of barrel shape of copper forgings, which differ quantitatively and sometimes even qualitatively from regularities of formation of barrel shape of steel forgings, all other conditions being similar. Such difference still remains insufficiently investigated.

Analysis of the latest investigations and publications The upsetting operation with including of application of different configurations anvils corresponds largely to one of the principles of design of energy efficient die-forging technologies – the principle of maximum of free non-contact surfaces formulated by I.M. Volodin [3]. Deformation is accompanied with formation of barrel shape of forgings, i.e. forming of the profile of side surfaces, thus allowing to offer a series of die-impression free methods of preliminary profiling of forgings [4]. In order to predict deformation in shape some data are usually used, obtained at upsetting of lead specimens, applied for physical modelling of the processes of hot deformation, despite their being slightly erroneous. Such approach does not take into account a quantitative difference in dimensions of side profile of forgings, made of different materials at different deformation conditions [5, 6]. It can lead to the wrong specifying of the line of dies parting, not complete filling of impressions with metal, excessive metal run out into fin and increased wear of dies. That is why for simulation of the processes of upsetting in order to ensure adequate reflection of the picture of shape deformation the dependencies of stresses on deformations at specified deformation rates and temperatures are obtained experimentally beforehand [7, 8], to be subsequently used for packages of finite-elemental analysis. The difference in indices of barrel shape at upsetting of forgings, made of different materials can be explained by objective reasons. First, due to the difference in friction indexes on the contacts of materials of “steel-copper”, “steel-lead”, “steel-steel” type, it seems quite difficult to single out influence of such factors like temperature, rate and degree of deformation, dimensions of forgings[9]. Metal pressure upon the tool at the process of upsetting is not constant either. Second, the quantitative indices are influenced by reological properties of the material i.e. the shape of the strengthening curve at the specified thermal and mechanical conditions [10]. Classical views, based upon the principles of continuity of volume and the least resistance do not take into consideration the influence reological properties of materials upon the ultimate shape deformation, the difference in which is explained only by different contact friction coefficients and, hence, different volume of metal, involved into rigid peripheral areas and also different dimensions of deformation centers [5, 6]. Now, the opinion that the influence of materials properties upon deformation of shape should not be neglected



seems to be prevailing [9, 10]. Investigations of the processes of materials deformation, based on copper at increased temperature ranges are available now [11], they helped to modify the technology of manufacturing of round shaped parts, to be used in electric engineering. The work [12] presents an analysis of the influence of the original shape of the side surface of copper forgings and conditions of contact friction upon the final shape deformation of the semi-finished product, special friction charts and methods of defining an optimal shape of the side profile of forging prior to upsetting being offered for practical application. It is worthwhile mentioning here that such investigations were carried out for conditions of cold deformation at room temperature of forgings only, while the aforementioned method seems to be difficult to be implemented in practice, due to difficulties in preliminary profiling of forgings for a concave profile of side surface. The work [13] describes the investigation of regularities in formation of barrel shape of forgings, manufactured of copper of М1 grade at upsetting in cold (18 C) and hot (850 С) states. The regularities obtained are to be taken into consideration for design of energy resources saving technologies of die-forging of round-shaped forgings in order to achieve a rational shape of the side profile of preliminary semi-finished products. The work’s objective, targets setting The objective of this work is the development of alternative low-waste technologies of hot die-forging of copper axially symmetric forgings on the basis of establishing rational modes of preliminary upsetting of work-pieces. The following problems are to be solved for achievement of the setting target:

- to develop a generalized method of technologies deign of combined die-forging of axially symmetric forgings which manufactured from non-ferrous metals on the basis of the model of barrel shape forming of work-piece with due regard to a possibility of combining the operations of upsetting, broaching, preliminary and final die-forging;

- to modify the technology of hot die-forging of axially symmetric copper, with due regard to special production conditions.

Investigation materials It is known that forging equipment for obtaining ordinary steel forgings should have one-three impressions, while for complicated forgings up to five impressions are required, including upsetting [1]. Application of multi-impression machines is often not necessary for die-forging of non-ferrous metals, as after each single operation it is required to remove defects on the surface of forgings [2]. As a rule, two methods of pressed die-forging are used [2]:

a. from a preliminary prepared forging, manufactured by open forging with application of flat or shaped heads;

b. from a dimensioned forging without any preliminary preparation. In the first case a prepared forging is stamped in a die with one impression with one or more heatings.

Filling of the die with metal depends upon the shape of the semi-finished product and die impression, while deformation charts should be chosen, so that they could ensure obtaining of the required shape due to pressing out, rather than upsetting [2], it also being a characteristic feature of technologies of die-forging of parts of non-ferrous metals. Multi-pass die-forging is carried out in one die or several special preliminary dies, which gradually lead the shape of forgings up to the required final shape. Preliminary passes



are evaluated just like for forgings, stamped from structural steel. Here, preliminary upsetting of copper forgings for die-forging is accompanied with intense formation of barrel shape of the forgings (see Fig.1), thus promoting better filling of impressions, i.e. promoting profiling of the forgings.

а) b) Figure 1: A typical barrel shape of a cylindrical forging at upsetting [6, 14]:

а – being the shape and dimensions of the upset forging; b – changes in barrel shape index, here = b) depending upon the increase of the current of contact index DT/Hk,

received by Y.M. Okhrimenko [6] for lead forging

Engineering evaluations of the processes of upsetting are connected with defining of the final shape of the upset forging. Unevenness of deformation at upsetting is usually evaluated, according to the barrel shape index diagram (see Fig. 1), designated by Ya.M. Okhrimenko with b [6] symbol, and according to A.V. Rebelskiy with [14] symbol:

%100/ zbb VV . (1)

where zV – is the forging’s volume;

bV – the volume forming a barrel shape (see Fig. 1, а). The regularity of formation of a barrel shape at upsetting (Fig. 1, b) is characterized by growth and subsequent decrease at the process of reduction and can be described by the expression, proposed by Ya.M. Okhrimenko [6, 14]. For determination of b the authors [6, 14] suggest application of experimental diagrams (Fig. 1, b), obtained for conditions of upsetting of lead forgings, it leading to errors in predicting shape deformation in forgings, manufactured from different materials. Or they apply complicated approximate empiric dependencies, describing the obtained family of curves and valid for 00 / HD 5 [6, 14]:

002

15.00

0

0

0

0

0

/1

06.01.01155

HDa

aHD

HD

HD

а

b

; 0

0

HD

HDa

k

id . (2)

This analytical description of the graphical dependence (see Fig. 1, b) does not consider the influence of metal temperature, its chemical composition, forces of friction, on the contact surface, rates of deformation, it often leading to substantial excessive



consumption of copper and makes predicting of unevenness of deformation at upsetting a complicated matter. The authors proposed in [13, 15] improved methods and software for prediction of formation of a barrel shape at upsetting of forging, made of commercial copper grades. Approaches, described in [16] were applied for description of the functional state of barrel shape formation of copper specimens, there attention was paid to a typical likeness of the experimental curves and the curves, corresponding to Plank’s law of radiation, known in thermal physics, which is described by a simple exponential expression. Hence, the complicated equation (2) can be replaced by a simple exponential function, which can be expresses in general view, with regard to boundary conditions like [13, 15]:

0

02

1

0

00

НD

НDaa

k

idb

k

id

eНD

НDa , (3)

where bxY )( (%); kid НDx / ; 000 / HDx ;

0a , 1a , 2a – are empiric coefficients, determined after the analysis of experimental results, i.e. taking into account the experimental conditions. The expression [13, 15]: corresponds with a big degree of precision to the law of normal distribution with asymptotic. It was suggested to perform the selection of coefficients 0a ,

1a and 2a as well as construction of the functions of barrel shape formation by means of a special computer program on the basis of the results of the experiment for investigating of copper forgings upsetting (М1) [13, 15] The program allows performing graphical construction of the functions of barrel shape formation with different initial contact indexes ( 00 / HD ) (Fig. 2) [13, 15].

Figure 2: Screen-diagram taken from the software intended for determination of barrel shape formation following hot upsetting of copper forgings with different initial contact indexes (D0/H0)

Fig. 3 represents the analytical model of formation of a barrel shape of a forging at upsetting and a combined graph for determination of barrel shape formation indexes at hot and cold upsetting with flat plates of copper (М1 grade) forgings with different values of the contact indexes. The original forging is understood to have been idealized with initial diameter 0D and 0H height. The barrel shape index is changed alongside with the growth in deformation at upsetting.



а b

Figure 3: Barrel shape configuration of copper forgings at upsetting: а – balance of forging’s volumes at upsetting with flat plates: C – deflection of the barrel generatrix; Db, DT, Dид – the final diametric dimensions; Vb, V1 и Vcm – the final volume

characteristics and displaced volume of a forging, b – alternations of the barrel shape index at the process of upsetting at different initial values of the contact index (D0/Н0): 5 – 18 С, D0/Н0 = 1.899; 6 – 18 С, D0/Н0 = 1.026; 7 – 18 С, D0/Н0 = 0.65;

8 – 18 С, D0/Н0 = 0.502; 9 – 850 С, D0/Н0 = 1.917; 10 – 850 С, D0/Н0 = 1.034; 11 – 850 С, D0/Н0 = 0.676; 12 – 850 С, D0/Н0 = 0.511

Correspondingly, index required for engineering evaluations of changes in shape for material at specified conditions of deformation depends upon the initial value of the contact index 00 / HD and the degree of deformation at upsetting 00 / HHH k ,

which can be expressed by means of the current contact index kid HD / , where

1/0DDid – an ideal diameter at uniform upsetting of a forging, hence,

10HH k – is the final height of the forging after upsetting.

Similarly to the expression (3), the family of curves 00 /;/ HDHDf kidb is described quite satisfactorily by the exponential model of alternation of barrel shape at upsetting, expressed through the degree of deformation:

1

)1(

1exp1)1(

12

30

02

23

0

00

1

HD

aHD

a

a

. (4)

After treatment of the experimental data for conditions of hot (850 С) upsetting of copper (М1) forgings the dependences of such coefficients from the initial value of the contact index were received:

.211.0;388.0

;88.39/674.24/384.80000 /488.0

2/495.0

1

002

000НDНD еaеa

НDНDa (5)

The average error between evaluations of barrel shape index by (4) model with regard to dependence (5) and the experimental data for М1 copper was 13 %. Comparison of the values of index for geometrically similar forgings, upset up to the same degree of upsetting under different conditions showed that calculations, performed in accordance



with the model, suggested by Ya.M. Okhrimenko [6] at hot upsetting of copper led to a degrease in results up to 6 % (it should be noted that for cold upsetting of copper the drop up to 44 % was observed). After evaluation of parameter the final dimensions are calculated:

01.01 idT DD ;

1

01.0101.01

43

TDС CDD Tb 2 . (6)

Technology 1: Die-forging of a billet of “Nozzle” type. At the press shop of PJSC “Azovstal”, belonging to the structure of the works’ mechanical department forgings of “Nozzle” (№ 041462-4, material-copper of М1 grade) for air blast water-cooling lances of the blast-furnace shop are manufactured. The lances are replaceable, manufactured by die-forging and welding. According to one of the variants of the obsolete technology “Nozzle” type forgings were to be manufactured on 25 MH hydraulic pressing unit, from a billet 8.85 kg in weight, heating was performed in a chamber furnace up to 850 0С. Die-forging was performed in flat position; the forging’s axis was place in horizontal plane that was the reason of designating laps for the holes. For subsequent mechanical treatment up to the required dimensions of the work-piece (see Fig. 4), the weight of which is 4.8 kg, the forgings were passed to mechanical and repair department of the Works. On the basis of the methods proposed in [13, 15] a new technology of die-forging of a copper billet of a “Nozzle” type was proposed with changes of the forging’s design (or without changes in the forging’s design) and application of upsetting with free shape changing of the side surface of the part, with subsequent broaching of the hollow with a conical punch for formation of laps from holes, used at technological passes (Fig. 4). The drawing of nozzle’s forging was symbolically divided into two sections: a short core, 51 mm in length and 88 mm in diameter and a conical one, 69 mm in length and 114 mm in maximal diameter (see Fig. 4 and Fig. 5). In order to ensure formation of the conical part of the forging at broaching with a conical broacher it is necessary that the diameter of the barrel of the extruded forging should be at least bD = (114+88)/2 = 101 mm (see Fig. 5). According to the shape deformation in accordance with the proposed scheme (see Fig. 5), the forging’s volume is equal to 939.59 mm, i.e. at copper density 8.940 kg/m3, the finished forging of “Nozzle” type is 8.4 kg in weight. At the forging’s diameter D = 87 mm the length of the original forging, evaluated on the condition of preservation of the volume will be: L = 224 mm. Then, length of the extruded section H = (224-51) = 173 mm, i.e. the initial index will be equal to HD / = 87/173 = 0.503.



Figure 4: The working copy of the part of “Nozzle” 041462-4 type

Figure 5: Passes in die-forging of “Nozzle» type: 1 – the forging; 2 – the upper stamp with the broaching unit ; 3 – the lower stamp;

4 – the broaching unit of the lower stamp (optional) ; 5 – the hollow of the lower stamp or replaceable extension for precision die-forging

By admitting the dimension of bD = 102 mm and TD = 88 mm, we shall eventually have [6, 14]:

1

1188

2388102 /

b

b

, (7)

whence /b = 0.1825, i.e. the index of barrel shape b = 18.25 %.

Applying the graph (see Fig. 3), we shall find that at b = 18.25 % and HD / = 0.503 the

value of the current contact index kid HD / = 1.0. Taking into account that:



)1(0 HH к , (8)

we’ll get:

23

1

1

0

0

HD

HD

k

id . (9)

Then, let us write:

23

1

1503.01

, (10)

whence = 0.37 or 37 %. Correspondingly, the height of the extruded section of the forging, prior to broaching will be equal to 10HH k = 173 (1 – 0.37) = 108 mm. With the aim of enlarging the possibilities of controlling filling of metal in the area of formation of the inserted part of the nozzle with 114 mm, it was recommended, at the level of a technological proposition, for manufacturing of such parts, to apply non-uniform heating (e.g. by induction method) or unilateral sub-cooling of the back butt of the forging prior to upsetting. At that it is necessary to observe the condition, according to which zone temperatures of heating should be directly proportional to the corresponding areas of cross sections of the forging [17, 18]. At uniform heating of the forging its lower part is inserted into the lower stamp, the depth being 51 mm with the aim of forming the core section of the forging. The original diameter of the forging was supposed to be equal to 87 mm in order to ensure its centering inside the space of the lower stamp, 88 mm in diameter. Formation of the conical section of the forging is possible both by means of open broaching with expansion of the butt section due to conical shape of the broaching unit and by shape formation inside the lower stamp, or inside the stamp extension. The latter option ensures better precision of forgings and seems to be more preferable. The final choice of the option is determined by the required quantity of forgings. This improved technology allows, at the pressing shop of PSC “Azovstal”, to diminish the forgings weight at die-forging from 8.85 kg to 8.4 kg At that saving of M1 copper was equal to 5.08 %, coefficient of metal application at die-forging was increased from 0.542 to 0.571. Technology 2: Die-forging of forgings of “Oxygen lance head” type Hot die-forging of copper (М1) forging at the pressing shop of PJSC ”Ilyich Iron and Steel works of Mariupol” (at present the shop is incorporated into Company Ltd. “METINVEST - Mariupol Mechanical Repair Plant”) is done after cutting of copper wire 90 mm into measuring sections 0H = 119 mm in length. Cutting is performed in the stamps of a crank pressing unit with nominal force 4 MN. Production control is performed with a ruler and a trammel after visual inspection. The cut-off measuring sections are passed to heating furnaces of the forging department. According to the technological chart the sections are heated inside the gas furnace of chamber type up to t = 850…900 С, then they are upset and broached in a jar washer. After that the forgings are heated and undergo preliminary forging. Upsetting, broaching and preliminary forging in movable anvil that fixed in the overarm of a forging manipulator is done with an air-steam forging hammer in accordance with the above-mentioned recommendations. For final die-forging the forgings are passed to the crank press (nominal force 4 MN). Formed fins (flash) are removed mechanically. With regard to the fact that broaching of forgings is done after upsetting, the formula of A.V. Rebelskiy [14] for evaluation of the final outside diameter ( D ) of the broached forging was written like this:



2)/(1 idprid DdDD , (11)

where d is the diameter of the broaching unit;

kprpr Hh /1 – a conventional degree of deformation at broaching, here prh – is thickness of the forging’s bottom at blind broaching. Whence, from all rearrangements we obtained:

22

201

dDD

pr

. (12)

The diameter of the forging after broaching should be at least 3…5 mm. Smaller than the diameter of the impression of stamp’s preliminary die-impression, which is 150 mm (diameters of a forging, fie-forged inside this die-block, see Fig. 6, d). Thence, it was understood that D = 147 mm (Fig. 6, c).

а b c

d e

Figure 6: Sketches of stamping passes for a forging of “Oxygen lance head” type : а – being measuring section, b – a forging following upsetting, c – a forging after broaching,

d – a forging after preliminary die impression, e – a forging after the final die impression Taking into consideration the conditions of copper delivery, the evaluations were carried out with preservation of the diameter of the original forging 0D = 90 mm (Fig. 6, а), and also the diameter of the broaching unit d = 42 mm (Fig. 6, c). At through broaching

pr = 1. Then, after calculations, according to (12) formula, we’ll have = 0.58 (i.e.

58 %), from where we got idD = 139 mm. The volume of the impression for a forging is equal to V = 744000 mm3. Then, the final height of a forging after upsetting:

2785.0/ idk DVH = 744 000/0.7851392 = 49 mm.



It allowed us to calculate the initial height of the forging

1/0 kHH = 49/(1 – 0.58) = 117 mm.

We also evaluated kpr Hh / = 0 и idDd / = 0,302 relation. Applying Tscheile’s graph (to

be found in [19, pp. 332]), we found kprk HH /. = 0.99, where prkH . – is the height of the forging after broaching. The evaluations were checked following the condition of formation of a barrel shape during upsetting and its development at broaching. The relation 00 / HD = 90/117 = 0.77

and kid HD / = 139/49 = 2.83. Then, according to relations (4) and (5) we obtained the index of barrel shape formation = 0.207. By performing calculations according to the formulae (6), we obtained TD = 124 mm, bD = 146 mm (Fig. 6, b).

From that pr = 0.208. The dimensions of a broached forging are prkH . = 48.5 mm,

TD = 124 mm, D = 147 mm (see Fig. 6, c). The equivalent index of fullering under these conditions is equal to poK = 1.113, it corresponding to forming or pinching die impression [1]. Thus, we confirmed that a deformed forging can be easily placed into the impression of the preliminary die (Fig. 7). Let we shall note here, that according to the conventional technology = 0.55. The actual length 0H = 117 mm, the difference from the conventional technology is 2 mm. Barrel shape formation ( pr ) at broaching was taken into account:

3 . / kprkpr HH

. (13)

Die-forging according to this improved technology (see Fig. 7) has been implemented at the forging-and-pressing shop of PJSC ”Ilyich Iron and Steel works of Mariupol” (now is Company Ltd. “METINVEST - Mariupol Mechanical Repair Plant”). There, forgings were die forged on a crank press inside closed stamps up to the dimensions, there being no fins formation. The developed processes allowed to reach saving of copper (М1) up to 7.7 %.



а b

c

Figure 6: Industrial implementation of die-forging of “Oxygen lance head» type: а – a forging and preliminary upsetting; b – broaching and a broached forging;

c – preliminary and final die-forging (photographs of the equipment and forgings)

Conclusions Generalized methods of creation of the processes of combined die-forging of axially symmetric forgings were developed, taking into account the regularities of shape formation of semi-finished products at preliminary operations and broaching. These methods are adapted to for die-forging of copper forgings with due regard to formation of barrel shape of copper forgings at preliminary upsetting. Advanced alternative technologies of die-forging of forgings of “Nozzle” and “Oxygen lance head” types, implemented at industrial enterprises allowed to reach copper saving up to 5…7.7 % of copper per each article. References [1] E.I. Semenov. Kovka i shtampovka tsvetnykh metallov [Die-forging and stamping of

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temperaturnogo polya neravnomerno nagretoy pod line zagotovki v shtampe [Modelling of temperature field of a non-uniformly heated along its length forging at its cooking inside the die], Vestnik PGTU: zbornik mauchnykch trudov [Bulletin of Priazovskyi State Technical University: a volume or research works], Mariupol, PSTU, vol. 17, pp. 125-129, (2007)

[18] V.V. Kukhar and V.A. Burko. Matematicheskaya model teplovykh processov v shtampe i ostyvayushey neravtomerno nagretoy zagotovke [Mathematical model of thermal process in a die and inside non-uniformly heated work-piece], Tezisy mezhdunarodnoy nauchno-technicheskoy konferentsii “machiny I plasticheskaya deformatsia metallov”, posvyaschennaya 100-letiuy so dnya rozhdeniya S.Z. Youdovicha [Theses of the International scientific and technical conference “Machines and plastic deformation of metals”, dedicated to 100th anniversary of S.Z. Youdovich], Zaporozhie, Zaporozhskiy National Technical University, pp. 37-38. (November 20-23, 2007)

[19] I.Y. Tarnovskiy, A.A. Pozdeev O.A. Ganago et al. Teoria obrabotki metallov davleniemI [Theory of plastic working of metals], Metallurgizdat publishing house, 672 p., (1963).

[20] V.V. Kukhar; O. V. Vasylevskyi, Form Changing and Stress-Strain State at Different Modes of Stretch Forging of Billets with Rotation in Combined Anvils, Volume 5, HCTL Open Science and Technology Letters (STL), June 2014, ISSN: 2321-6980, ISBN: 978-1-62951-400-0.

[21] E.Yu. Balalayeva; V.V. Kukhar; O.V. Hrushko, The Computer-Aided Method of Calculation of Universal Elastic Rotary Compensator for the "Press-and-Die" System Errors of Crank Press for Drawing-Forming Operations, Volume 6, HCTL Open Science and Technology Letters (STL), August 2014, ISSN: 2321-6980, ISBN: 978-1-62951-779-7.

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